How to Remove Duplicates in Drupal Views with Taxonomy Relationships

When working with Drupal, one of the most powerful tools at our disposal is Views. It offers a flexible way to present content, especially when content is associated with taxonomies. However, sometimes we encounter an annoying issue: duplicates. I personally faced this challenge today.

The Problem:
I created a Drupal View named ‘resources’. In this view, I display items along with their associated taxonomy terms, thanks to the relationships I’ve established. I’ve also enabled exposed taxonomy filters, allowing users to easily filter through the content. However, I noticed an issue: some items appear multiple times because they’re linked to several taxonomy terms.

I tried the “Distinct” and “Aggregate” options in Drupal Views, hoping for a quick fix. However, they didn’t solve the problem. So, after some digging, I found a solution that worked, which I’ll share below.

How to Fix It:

1. Add a Unique Identifier to Each Item:
   First, go to your ‘resources’ view in Drupal. Add the field Content: id to the view.
2. Alter the View’s Query:
   Implement a custom hook to modify the query of the view. This will ensure results are grouped by the content’s unique ID.

/**
 * Implements hook_views_query_alter().
 */
function my_module_views_query_alter(ViewExecutable $view, QueryPluginBase $query) {
  // Target the 'resources' view.
  if ($view->id() == 'resources') {
    // Add the nid field with a groupby function.
    $query->addField('node_field_data', 'nid', '', ['function' => 'groupby']);
    // Group results by node ID.
    $query->addGroupBy('node_field_data.nid');
  }
}

In Simple Words:
What we’re doing here is simple. We tell Drupal to look at each entry in our view and group them by their unique content ID. This way, even if a piece of content is related to multiple taxonomy terms and would normally appear more than once, it will now show up only a single time.

Happy debugging!